Administration of therapeutic or diagnostic agents to a subject is typically accomplished by either localized or systemic routes. With many types of agents, localized delivery methods are desirable. For example, medical compounds of interest may have desired diagnostic or therapeutic effects within the region into which they are introduced, but also exhibit toxic or other undesirable effects when they are allowed to circulate elsewhere. In certain cases, it is desirable to introduce a higher volume of a compound to the local region than can be tolerated by other body tissues if that volume were to ultimately cause the systemic concentration to exceed a safe threshold.
A common example of such a compound is radio-opaque dye. Iodinated forms of such a dye are used routinely during catheter-based interventional procedures such as coronary, renal, neurological and peripheral arteriography. The iodine component has a high absorption of x-rays and therefore provides a contrast medium for the radiological identification of vessels when introduced within an upstream artery. However, the use of such dyes is known to have potential toxic effects depending on the specific formulation, including direct injury to renal tubule cells, endothelial injury, bronchospasm, inflammatory reactions, pro-coagulation, anti-coagulation, vasodilation and thyrotoxicosis.
Other materials that may be introduced locally for desired effects but whose direct or other effects would be undesired elsewhere include vasoactive agents, cytotoxic agents, genetic vectors, apoptotic agents, anoxic agents (including saline), photodynamic agents, emboli-promoting particles or coils, antibodies, cytokines, immunologically targeted agents and hormones.
An important anatomic concept with respect to the vasculature and other conduits supplying and draining an organ is the principle that a tissue or organ and regions of the organ have a limited number of primary supply conduits and a limited number of draining conduits. Material introduced into the upstream side of the target tissue will typically be dispersed among the diverging arterioles and capillaries, which then reconverge into a collection of common venules and vein(s) downstream, e.g., in a physiological efferent fluid collection site. For example, the myocardium of the heart is fed by the right coronary, left anterior descending and left circumflex arteries. Each of these arteries enters a capillary network that eventually converges into the small and middle cardiac vein, anterior interventricular vein and posterior vein of the left ventricle. These veins are all tributaries of the coronary sinus, which may be viewed as a cardiovascular efferent fluid collection site. Material introduced into any of the aforementioned coronary arteries that travels through the capillary network will enter the coronary sinus providing an opportunity to collect it before it returns to the systemic circulation. In another example, the brain is fed by the carotid and vertebral arteries which enter a highly anastomotic network. Blood flow through the brain substantially drains to the systemic circulation via a network of sinuses that converge onto the internal jugular veins. In yet another example, each kidney is substantially supplied by a renal artery and drained by a renal vein. In yet another example, a tumor or metastatic lymph node may have a set of primary afferent (supply) conduits and a set of primary efferent (drainage) conduits. In yet another example, the lungs are supplied by a pulmonary artery and its branches, and are drained by the pulmonary veins and their tributaries into the left atrium.
As indicated above, there are many instances where localized delivery of an agent is desired. Of particular interest in certain situations is the localized delivery and then subsequent removal of an active agent in an administration approach which would limit the systemic exposure of a subject to an agent even more effectively than localized delivery alone. The present invention satisfies this need.